1. Field of the Invention
The present invention relates to an electrode with low hydrogen overvoltage which is used in an electrolysis of an aqueous solution and the process for preparing said electrode.
2. Description of the Prior Arts
Various anticorrosive electrodes have been used in electrolysis of aqueous solution to obtain an electrolyzed products such as electrolysis of an aqueous solution of an alkali metal chloride to obtain an alkali metal hydroxide and chlorine.
When an overvoltage of the electrode used in an electrolysis of an aqueous solution such as an aqueous solution of alkali metal chloride or water is lowered, the electric power consumption can be reduced and the electrolyzed product can be obtained at low cost.
In order to reduce a chlorine overvoltage of an anode, various studies have been made on the materials of the substrate and the treatments. Some of them have been practically employed.
It has been needed to use an electrode having a low hydrogen overvoltage and an anticorrosive characteristic since the diaphragm method for an electrolysis using a diaphragm has been developed.
In the conventional electrolysis of an aqueous solution of an alkali metal chloride using an asbestos diaphragm , iron mesh has been used as a cathode.
It has been proposed to treat a surface of an iron substrate by a sand blast treatment in order to reduce a hydrogen overvoltage of the iron substrate (for example, Surface Treatment Handbook Page 541 to 542 (Sangyotosho) by Sakae Tajima). However, the asbestos diaphragm method has disadvantage of a low concentration of sodium hydroxide as about 10 to 13 wt. % and a contamination of sodium chloride in an aqueous solution of sodium hydroxide. Accordingly, the electrolysis of an aqueous solution of an alkali metal chloride using an ion exchange membrane as a diaphragm has been studied, developed and practically used.
In accordance with the latter method, an aqueous solution of sodium hydroxide having high concentration of 25 to 40 wt. % may be obtained. When the iron substrate is used as a cathode in the electrolysis, the iron substrate is broken by stress corrosion cracking or a part of the iron substrate is dissolved in a catholyte because of high concentration of sodium hydroxide and high temperature such as 80.degree. C. to 120.degree. C. in an electrolysis. British Pat. No. 1,148,865 discloses that low overvoltage electrode is obtained with codeposition of metal particles, for example, Raney nickel and nickel from suspension which comprises metal particles suspended in the same metal containing solution. The similar disclosure is found in U.S. Pat. No. 4,170,536. However, the electrolytic characteristics of these electrodes is not satisfactory for use in practice. Namely, such electrode is poor in activity and the adhesion of the particles to the bonding metal is not enough so a characteristics deteriorates during a short period. This is because, in these prior art, said solution is so called Watt bath containing low concentration of chlorine ion. So, these electrodes contain particles, the oxygen content of which is very large, resulting low activity and low adhesion strength of said particles.